Add Ctrl+Shift+F Markdown formatter command

[mvogttech]

Summary

• add a Ctrl+Shift+F shortcut that reformats the current document using a new Markdown formatter
• update the editor buffer to accept external content updates and track history when formatting is applied
• document the shortcut and configuration along with unit tests covering the formatter and config defaults

Testing

• npm test -- tests/unit

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https://chatgpt.com/codex/tasks/task_e_68f0765b9bc483308febcb240d24fd80

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve Markdown hard line breaks

The formatter unconditionally removes trailing whitespace from every line (rawLine.replace(/\s+$/, '')). In Markdown, a line ending with two spaces is a deliberate hard line break and should be preserved. Running Ctrl+Shift+F on content that uses this convention (e.g. "First line␠␠\nSecond line") will erase the spaces and change the rendered output by merging the lines. The formatter should either keep the double spaces or translate them to an explicit <br>/\ escape instead of stripping them.

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